Returns frame content type.
Return actual frame's content type. Return value can be a NULL value which means this frame has no content type defined. You must not free returned value.
|frame ||The frame where the content type will be returned.|
- the content type if defined or NULL if not. On error, NULL also is returned. Only one error is check, if frame is not NULL. If you don't want to fall in the same case of having a correct frame with no content type and having a wrong frame (NULL value) you should check if frame is not NULL first.